It really depends on what you will use it for.
I have a windows PC as a main computer and both an iPad (both a brand new mini and full size iPad 4, both cellular versions) and a macbook air. The iPad is fine for a mobile device if you mostly just want to browse the web, watch videos, play iPhone type game on a big screen and send/receive emails. However, if you actually need to be productive out of the home, while possible on an iPad, it is much easier on a macbook. I used only the iPad 4 as my mobile device from the time it came out until September of this year when it started to get really slow, so I bought the macbook air. I ended up getting a new iPad mini too. Having both, I find now that if I am not in my office, I am more likely to reach for the laptop. It is just easier to use and I can have multiple things on the go, unlike on an iPad. I mostly end up using my iPad for netflix and games, and surfing the web on the go (while sitting on the train everyday).
The MacBooks don't have cellular, which gives a cellular iPad an advantage. It is very convenient to be anywhere and still be connected and have a screen large enough to actually be able to see. But the iPad is limited in that it is more an entertainment device. If I didn't have to sit on a train everyday for two hours (of if I had an iPhone 6+), I would never use my iPad. Of course you can tether your phone to your laptop, but on a crowded train setting that up is a bit of a juggling act. I bought the mini so that I could cary both it and the macbook, because now that I have the laptop, I wouldn't want to go back to iPad only as a mobile device. It is just way more hassle to type out and edit a document, do compose longer emails, and on iPad it is difficult to Skype and have a file open (for example if they send you a photo and you open it, on an iPad you will still hear them, but not see them, but on a mac, a little bow with their face follows you to others applications).